// Single-byte codec. Needs a 'chars' string parameter that contains 256 or 128 chars that
// correspond to encoded bytes (if 128 - then lower half is ASCII). 

exports._sbcs = function(options) {
    if (!options)
        throw new Error("SBCS codec is called without the data.")
    
    // Prepare char buffer for decoding.
    if (!options.chars || (options.chars.length !== 128 && options.chars.length !== 256))
        throw new Error("Encoding '"+options.type+"' has incorrect 'chars' (must be of len 128 or 256)");
    
    if (options.chars.length === 128) {
        var asciiString = "";
        for (var i = 0; i < 128; i++)
            asciiString += String.fromCharCode(i);
        options.chars = asciiString + options.chars;
    }

    var decodeBuf = new Buffer(options.chars, 'ucs2');
    
    // Encoding buffer.
    var encodeBuf = new Buffer(65536);
    encodeBuf.fill(options.iconv.defaultCharSingleByte.charCodeAt(0));

    for (var i = 0; i < options.chars.length; i++)
        encodeBuf[options.chars.charCodeAt(i)] = i;

    return {
        encoder: encoderSBCS,
        decoder: decoderSBCS,

        encodeBuf: encodeBuf,
        decodeBuf: decodeBuf,
    };
}

function encoderSBCS(options) {
    return {
        write: encoderSBCSWrite,
        end: function() {},

        encodeBuf: this.encodeBuf,
    };
}

function encoderSBCSWrite(str) {
    var buf = new Buffer(str.length);
    for (var i = 0; i < str.length; i++)
        buf[i] = this.encodeBuf[str.charCodeAt(i)];
    
    return buf;
}


function decoderSBCS(options) {
    return {
        write: decoderSBCSWrite,
        end: function() {},
        
        decodeBuf: this.decodeBuf,
    };
}

function decoderSBCSWrite(buf) {
    // Strings are immutable in JS -> we use ucs2 buffer to speed up computations.
    var decodeBuf = this.decodeBuf;
    var newBuf = new Buffer(buf.length*2);
    var idx1 = 0, idx2 = 0;
    for (var i = 0, _len = buf.length; i < _len; i++) {
        idx1 = buf[i]*2; idx2 = i*2;
        newBuf[idx2] = decodeBuf[idx1];
        newBuf[idx2+1] = decodeBuf[idx1+1];
    }
    return newBuf.toString('ucs2');
}